An evaluation of bacterial source tracking of faecal bathing water pollution in the Kingsbridge estuary, UK.

In this study, Hussein et al. (2012) look at the microbial quality of water at South Sands, Salcombe. In the past, South Sands has experienced some faecal indicator bacteria (FIB) contamination; however it generally meets the requirements for European Union (EU) bathing waters. The beach is well known for human recreational activities.

Three samples of water and sediment from three locations were collected. One location was the beach; another was a pond just back from the beach and the last one a stream which runs into the sea. Human faeces were collected from healthy volunteers, whereas animal faeces were obtained from farms close to the study area. First of all membrane filtration was carried out, in order to detect and enumerate Enterococci, Escherichia coli and Bacteroides. DNA was extracted from the water and faeces samples for use in the Polymerase Chain Reaction (PCR), which was used to detect Bacteroides-Prevotella 16S rDNA gene in the water, sediment and faecal samples. Previously designed primer pairs were used.

The bacterial cultures showed that South Sands had ‘excellant’ values for FIB (Enterococci and E. coli) at all times of sampling. Water values of FIB and Bacteroides were higher in the stream than in the sea and higher still in the pond at all times. All sediment samples show a loading of both FIB and Bacteroides which also shows a significant increase out of the bathing season. The general Bacteroides primer set (Bac32F and Bac708R) confirmed that there were Bacteroides in all water, sediment and faecal samples. The human primer gave one positive result in the stream, while the cow primer gave a positive reaction with water and sediment from the stream and sediment from the beach. The horse and pig primers gave negative results.

This study revealed that the bathing water at South Sands was excellent based on the EU Bathing Water Directive 2006 for Enterococci and E. coli. The higher levels of bacteria in the stream and pond may be due to runoff from agricultural land, as it has previously been shown that this is a significant source of contamination. The increase in bacterial contamination in the sediment from the stream and pond, in comparison to the beach, is probably due to different sediment types, as the beach is composed of mobile sand. PCR was successful in showing although human faecal markers were not present on the beach; they were in present in the stream indicating a possible hazard for bathers, as the stream runs into the sea.

Overall, I think that this is a good study showing the successful use of microbial source tracking. More work needs to go into the specificity and persistence of Bacteroides markers in the environment, as this not known to any great degree. Once this has been confirmed, Bacteroides could be considered for a future EU Bathing Water Directive.

Hussein K.R, Bradley G, Glegg G. 2012. ‘An Evaluation of Bacterial Source Tracking of Faecal Bathing Water Pollution in the Kingsbridge Estuary, UK’. The Significance of Faecal Indicators in Water: A Global Perspective. Ed Kays and Fricker. Royal Society of Chemistry, UK.

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